Method of lapping gears



1 1947- I E. R. GASSER I 3 HETHQD OF LAPPING GEARS Filed Dec 3, 1945 INVENTOR. 5 m1 36-4-51 Patented July 8, 1Q47- METHOD OF LAPPIN G GEARS Emil R. Gasser, Buflalo, N. Y., assignor to Farrel- Birmingham Company, Inc., Buflalo, N. Y., a corporation oi Connecticut Application December 3, 1945, Serial No. 632,352

1 Claim. (Cl. 51-287) My present invention relates to a method of' lapping gears and pinions of the spur, single-helical and double helical types and aims to provide certain improvements therein.

Gear tooth contours as cut on a gear cutting or generating machine are composed of innumerable infinitesimal facets, and in order to elimi-- hate these small inaccuracies of machining and produce smoother and more precise tooth contours, the gears are subjected to a lapping procesS.

In the past, gears have been lapped by merely running the mating gear and pinion together with a lapping compound between the toothed surfaces. More recent practice consists in lapping the gears with lapping dummies which are simple cast iron gears proportioned as to tooth form to give a certain lapping action when meshed with a gear or pinion to be lapped, and using a suitable lapping compound. More specifically, current practice consists in taking one dummy lapping pinion and meshing it with the subject gear to be lapped and then operating the two together for a certain length of time. After this, another dummy lapping pinion of somewhat difierent tooth proportions is meshed with the same subject gear and again operated for a. cer- "tain length of time, usually the same as with the first dummy pinion. Finally, the subject gear that has been lapped is then meshe'd with the pinion that is normally supplied -with the gear and given a so-called final lapping for a certain period of time.

It is a well known fact that if a gear and a pinion, whether it be a dummy lapping pinion or a regular pinion are operated together with an abrasive lapping compound, a hump will develop on the gear teeth at points known as the pitch points where no sliding action or but very little sliding action takes place during gear op- 2 subject gear being lapped and on the lapping dummies regardless of the duration of the lapping operation.

The foregoing and other objects not specifically enumerated are accomplished by operating two lapping pinions simultaneously in mesh with the subject gear to be lapped, the pitch circles of the lapping pinions being so proportioned to the operating pitch circles of the subject gear that the corresponding pitch points are at difierent pressure angles. The invention will be better understood from the detailed description which fol.- lows when considered in connection with the accompanying drawing which is illustrative of the method, and wherein-'- Figure l is a diagrammatic side elevationof the arrangement of the subject gear to be lapped and the lapping pinions when carrying out the present invention.

Fig. 2 is an enlarged fractional side elevation showing the tooth action for high pressure angle lapping such as will be accomplished by the left hand lapping pinion of Fig. l.

Fig. 3 is a view similar to Fig. 2- showing the tooth action for low pressure angle lapping such as will be accomplished by the right hand lapping pinion of Fig. 1.

In carrying out the method of the present invention a subject gear ill to be lapped is shown in mesh with two dummy lapping-pinions l I and i2, the subject gear and the lapping pinions being mounted on spindles supported in bearings l3, l4 and i5, respectively. The bearings may be adjustably mounted upon a bed plate it or the like, and means (not shown) may be provided for driving the subject gear or the dummy pinions,

as desired. In Fig. 1 of the drawings, in lieu of eration. This hump constitutes a distortion of the necessary involute shape that is so essential ject the elimination of the hump at the pitch points of gear teeth by a lapping operation. A further object is to substantially reduce the time consumed for the lapping operation as compared with prior practice. complish the first two mentioned objects while A further object is to acmaintaining the involute form of the teeth on the showing the teeth of the subject gear and the lapping pinions, there is merely shown the root circles, the engaging pitch circles and the addendum circles of said respective gears. The teeth relationship of the subject gear and the lapping pinions are, however, shown in Figs. 2 and 3. In the gear Ill and pinions II and 12, the root circles are designated Ilia, Ila and 12a, and the addendum circles as Nib, lib and I222, respectively. The engaging pitch circle lie of the lapping pinion II is shown as providing for low pressure angle engagement with the gear l0 and as being tangent to th engaging pitch circle lllc of the subject gear Ill. The engaging pitch circle I 20 of lapping pinion'l2 is shown as providing for high pressure angle engagement with-gear l0 and as being tangent to the engaging pitch circle Hid of the subject gear l0.

amazes In Fig. 2 there is illustrated the relationship of the teeth on the lapping pinion l2 and the subject gear l whereby high pressure angle lapping is achieved. It will be noted that the adden- -dum of the teeth on the lapping pinion is relatively greater than on the subject gear and provides an engaging pressure angle between the teeth of about 22. In Fig. 3 the teeth relationship is such as to provide for low pressure angle lapping at a pressure angle of about 18". These the case illustrated in the drawings, the intended normal operating pressure angle of the subject gear with its regular pinion is approximately 20, wherefore, when such a,subject gear is operated in mesh simultaneously with pinions such as H and I2 with an abrasive lapping compound between the toothed surfaces, any hump which would normally build up at the pitch point of the teeth of the subject gear due to thehigh pressure angle lapping is immediately wiped clean by the low pressure angle lapping of the other pinion, and vice versa. Because of this action the tooth shapes of the lapping pinionsand the subject gear being lapped maintain their original involute shape accuracy and in fact even improve themselves.

After the subject gear l0 and the lapping pinions l I and I2 have been simultaneously operated in mesh with a lapping compound for a predetermined arbitrary length of time, the subject gear is given a final lapping treatment with the pinion, or a substantially identical pinion, that is normally supplied with the subject gear.

The lapping pinions are made as though they were regular gears in a conventional manner on gear cutting or generating machines, but for the purpose of economy I prefer to make them of cast iron.

From the foregoing detailed description it will be appreciated that with the present invention the objects recited in the opening statement of this specification are accomplished. These may again be summarized as follows:

(a) 'The time consumed for lapping is reduced to about one-half that required where only a single lapping pinion is used.

(b) The tooth shape of the subject gear and the lapping gears is maintained in involute form regardless of the duration of the lapping operation.

(c) The lapping plnions or dummies as they are termed tend to retain their original involute shape much longer than when used in lapping by the old method and can therefore be used without recutting to lap more gears than if they had been used singly.

In the foregoing description and in the claim it is to be understood that the terms gear and pinion are used synonymously and that either may be substituted for the-other without aflectin the scope of the invention. 4

What I claim is:

The method of lapping a gear to improve its tooth surface contour, said method comprising operating a subject gear to be lapped in mesh completely across the width of its teeth simultaneously with two lapping pinions with a lapping compound between the meshed toothed surfaces, providing an operating pressure angle between the teeth of one lapping pinion with the teeth of the subject gear which is greater than the intended normal operating pressure angle of said subject gear, and an operating pressure angle between the teeth of the other lapping pinion with the teeth of the subject gear which is lesser than the normal intended operating pressure angle of the subject gear, and so choosing said greater and lesser operating pressure angles that they diiTer from the normal intended operating pressure angle of the subject gear, by approxi- 'mately the same degree.

EMIL R. GASSER.

REFERENCES CITED The following references are of record in the file of this patent:

- Number UNITED STATES PATENTS Name Date 1,634,863 Allen July 5, 1927 2,114,616 Sykes Apr. 19, 1938 FOREIGN PATENTS Number Country Date 274,859 Great Britain Nov. 19, 1928 

